pondering candle molds

[zwol]

I've been making lots of candles this past month. They're all the same: two-inch-diameter, four-inch-high cylinder mold candles. It's been way harder than it ought to be, because your standard candle mold is crap.

Your standard cylinder candle mold, see, is made of two pieces of sheet steel. One piece is rolled into a cylinder and closed with a crimp seam plus a line of solder. The other piece is a flat square with the corners trimmed off; then all four edges are bent down to make feet, and a tiny hole punched in the middle. The cylinder is soldered onto the flat piece, making a cylindrical chamber. To use the mold, you thread wick through the tiny hole and out the open end of the cylinder, then tie it to a copper rod that will sit on top of the open end. You pull the wick tight underneath, cut it off, and seal the hole somehow (both holding the wick in place and preventing the wax from running out the hole).

Problem number one with this design is the hole in the bottom. No sealing method works adequately. I have tried disgusting gray sticky stuff (doesn't reliably stick to the bottom of the mold, almost impossible to get off your fingers); little bits of foam backed up by washers and knots (the foam's only good for two or three castings, doesn't reliably seal, wastes lots of wicking); little rubber spike thingies (great when they work, but often they just plain fall out); and Scotch tape (works better than any of the above, but still leaks).

Problem number two is cleaning. If the inside surfaces of the mold chamber are not spotlessly clean, the surface of the finished candle will have blemishes. However, the shape of the chamber makes it very hard to clean effectively, especially close to the bottom. And the bottom is the most important part, because that's the top of the finished candle. It doesn't help that very little dissolves wax. I have a bottle of patent wax remover, which is nasty volatile stuff that tends to evaporate before it can be cleaned off, leaving an invisible residue that, yup, makes blemishes on the next candle. One might be tempted to throw the things in the oven and bake off all the crud (which is mostly leftover wax dust) but this is a terrible idea: not only does it not work (you replace wax dust with baked-on carbon particles), but the solder typically used will melt in even a mildly hot oven, destroying the mold. Boiling water doesn't work either, because you can't get a continuous flow through the inside of the mold; it just picks up the wax and redeposits it again. And it can cause the mold to rust. Oh, and being made of sheet steel, the molds have edges that are just dying to give you nasty cuts, usually on the webbing between your fingers as you reach deep within the mold with a wad of paper towel.

Problem number three is air bubbles just under the surface of the finished candle. I'm not sure this is exactly the mold's fault. The bubbles seem to come from dissolved air in the wax. Increasing the pouring temperature helps (as this drives out the dissolved air); so does heating the mold before pouring (this discourages prompt crystallization at the outside of the mold, but I have no reason why that would make a difference). I don't like increasing the pouring temperature, because I have to set the wax pot directly on the stove to do it, which is dangerous — not as dangerous now I have an electric stove, but still.

Problem number four is the wrong cooling pattern. Wax shrinks a lot when it cools; you have to top up the mold a few times after the initial pour. Ideally, the wax would crystallize smoothly, evenly, slowly, and from the bottom up, remaining liquid at the top until the very end; one could then top up the mold with no special effort. What happens instead is, it crystallizes from the outside in, leaving a void in the middle with a thin skin over the top. You have to melt out the skin (I do this with a soldering iron) before topping up, which is tedious. Worse, because the wax has solidified around the outside all the way to the top, you get a discontinuity between the old wax and the new, making a visible line on the surface at the top of the mold (which will be the base of the candle). This is not just just a blemish in a place no one ever looks, it's also a weak point; if you try to carve things on the base of the candle you're likely to have great big chips come off, damaging your design.

Related to this is that the candle base never, ever comes out flat. I have a special widget just for flattening them after the fact. It's a big flat metal plate with a ring-shaped catch basin around the outside, that I sit on top of a pot of boiling water. If you set a candle on the flat surface, the bottom melts away wherever it's in contact, until eventually it's flat. There's two problems with this: first, it's one thing to get the bottom flat, but one also wants it square with the sides of the candle, which is hard to do by eye. My candles typically come out with a degree or so of tilt. Second, the wick (poking through the bottom where one cut it off after removing the candle from the mold) interferes;the best thing I've found is to gouge it out to a few millimeters below the target surface with a chisel, but this of course leaves a divot in the base, which (again) causes problems when you try to carve designs there.

I have vague ideas in my head for better molds. The cleaning problem might be addressed by making the mold in two pieces, say a solid block of metal for the base, with a threaded ring cut that the cylinder piece screwed into. This would force one to make the cylinder out of stamped tubing instead of rolled tubing, but that would be good, because then there wouldn't be a seam to make a ridge on the side of the candle. If the base were thick enough, one could have some sort of clamp embedded in it that would hold the wick, eliminating the need for an unreliably-sealed hole.

An insulating jacket of some kind might solve the uneven cooling problem. It would have to be an odd shape, kind of an inverted cone, to get the right temperature gradient going. Alternatively, one might make the entire mold out of one solid block of metal with embedded cooling-water channels, but this strikes me as far too complicated. Any sort of insulation will of course slow down the process enormously, but I see no way around that.

I don't have good ideas for the troublesome top surface (base). It would be nice if there were some magic way to suspend the wick a few millimeters below the upper surface of the molten wax; then one could simply insulate the top and be done. Ideas? How about the air bubbles, anyone got a magic bullet for that?

Comments

Plastic is fantastic

[lilpnkspyder.livejournal.com]

I hate those damn metal molds. The best solution is to make your own. Any metal mold is going to be a bitch to work with, and the plastic ones just melt once the wax has been poured in, spilling the unhardened wax all over the damn place. Aargh. I suggest you head to your local plastics supply (I know TAP Plastics carries this stuff) and pick up some of that flexible (rubber?) mold casting compound. Here's what you do. You carve the candle form out of resin (specifically designed for that sort of casting) or you take a pre-existing form. You put the form in a coffee can (or similar vessel), cover the form with mold release spray, and pour the casting compound around it. Because the casting compound is flexible you should be able to pop the form (and subsequent candles) right out of the mold when they're dry with minimal inconvienience and personal injury.

As for the topping off, I've found that the ambient air temperature has a lot to do with how much shrinkage occurs at the base. The colder it is, the faster (and more) it will shrink. If you maintain a warm, even temperature, you won't have to top off barely at all. I suggest if you are going to try the casting method I outlined above, you make a few inches extra allowance on your resin form, so that you can just melt off the part where it will cool and get all sucked in.

Melting the bottom flat just sucks. I have a hard time with that part too. I suggest going around the candle measuring the desired length from the top with a cloth tape measure, and making pin marks in the base. Then you'll at least have some guiding marks that you'll know not to melt past.

Anyway, that's what I'd suggest. Plastic casting stuff is not cheap, but I think the trade-off in convienience would be worth it. Let me know what you decide to do.

And *hugz* :D

Re: Plastic is fantastic

[zwol.livejournal.com]

Ooh, nifty idea. (I had no idea you made candles!) It sounds like it would help with the uneven cooling, but I'm not seeing how it helps with the cleaning — in fact, wouldn't it make that part worse? Unless the rubber is so flexible that you can turn it inside out without it tearing? And how do you wick such a mold?

Unfortunately I have very little control over the ambient air temperature in my kitchen ... awkward layout, heater doesn't help for beans, and it's been pretty chilly lately. The voids in some of these candles went all the way to the bottom of the mold at first-repour time (90mins after initial).

Pin marks, good idea. Could help with keeping it square, too.

*hugs* I'll be in your part of the world for two weeks starting Thursday, by the way; you going to be around?

Re: Plastic is fantastic

[lilpnkspyder.livejournal.com]

God dammit! LJ ate my comment! Which took me a half hour to write because it was so informative!

Anyway, I will be out of town Fri-Mon for the big holiday, but I should have some time after that if you want to hang out. The best way toreach me is by cell phone after 5 pm. We can discuss more candle-making and plastic casting then, when I'm not stressed out or pressed for time. Hope to talk to you soon :)

Re: Plastic is fantastic

[zwol.livejournal.com]

Ugh. I hate it when that happens. *hugs*

I'll have family stuff over the big holiday as well. I'm afraid I've lost your cell phone number, could you email it to me please?

Oh air bubbles....

[lilpnkspyder.livejournal.com]

Try pouring slowly, that helps. Also, the higher the wax temperature, the more bubbles will be in your candle. You have to find a good balance between all the temperature ranges things can take (for the dyes, scents, mold, etc.) Takes some skill. I never quite mastered it myself.

Re: Oh air bubbles....

[zwol.livejournal.com]

Huh. My experience is exactly the opposite - higher wax temp makes fewer bubbles. This last time, after bubbles ruined an entire batch, I drove the pot temperature up to 250F and got much better results. Similarly, slow cold pours cause me trouble, the first dollop of wax hits the cold bottom of the mold, freezes with bubbles in it, and then doesn't remelt when more wax comes in on top of it. So I get both bubbles and crystal discontinuities at the bottom of the mold :(

A major confound, though, is that I was having to pour through filters because there was all this crud in the bottom of my wax pot; that slowed down the pour quite a bit, and I think the thin trickle of wax out the bottom of the funnel was more prone to absorbing air.

I don't do scented, so that's not an issue.